READ ONLY mode allows the storage engine to apply optimizations that cannot be used for transactions which write data. By default, transactions are in READ WRITE mode (see the tx_read_only system variable). The access mode specifies whether the transaction is allowed to write data or not. SELECT to block if other transactions have modified the selected rows,ĭistributed XA transactions should always use this isolation level. Serialized if performed as a consistent (non-locking) read and need It therefore is known to be read only and can be If autocommit is enabled, the SELECT is its own This level is like REPEATABLE READ, but InnoDB implicitly converts all This is the minimum isolation level for non-distributed XA transactions. Scanned, using gap locks or next-key (gap plus index-record) locks toīlock insertions by other sessions into the gaps covered by the range. For other search conditions, InnoDB locks the index range For a unique index with a unique searchĬondition, InnoDB locks only the index record found, not the gapīefore it. Statement uses a unique index with a unique search condition, or a UPDATE, and DELETE statements, locking depends on whether the Same transaction, these SELECT statements are consistentįor locking reads (SELECT with FOR UPDATE or LOCK IN SHARE MODE), Several plain (non-locking) SELECT statements within the Isolation level: All consistent reads within the same transaction read the There is an important difference from the READ COMMITTED This is the default isolation level for InnoDB. Also, record locks for non-matching rows are releasedĪfter MariaDB has evaluated the WHERE condition.If you use READ COMMITTED or enable innodb_locks_unsafe_for_binlog, you must use row-based binary logging. There is no InnoDB gap locking except for foreign-key constraint checking andĭuplicate-key checking. Level is used or the innodb_locks_unsafe_for_binlog system variable is enabled, Necessary because "phantom rows" must be blocked for MySQL replication and Range scanned, using gap locks or next-key (gap plus index-record) locks toīlock insertions by other sessions into the gaps covered by the range. For range-type searches, InnoDB locks the index Unique index with a unique search condition, InnoDB locks only the index recordįound, not the gap before it. Range-type search condition (such as WHERE id > 100). Unique search condition (such as WHERE id = 100), or a Statements, locking depends on whether the statement uses a unique index with a The gaps before them, and thus allows the free insertion of new records next to Or LOCK IN SHARE MODE), InnoDB locks only index records, not Seeįor locking reads ( SELECT with FOR UPDATE Transaction, sets and reads its own fresh snapshot. (non-locking) reads: Each consistent read, even within the same Read." Otherwise, this isolation level works likeĪ somewhat Oracle-like isolation level with respect to consistent Isolation level, such reads are not consistent. SELECT statements are performed in a non-locking fashion,īut a possible earlier version of a row might be used. The following sections describe how MariaDB supports the different transaction levels. Record-level locks and how it uses them to execute various types of statements, InnoDB supports each of the translation isolation levels described here transaction_isolation, transaction_isolation tx_isolation, tx_isolation įrom MariaDB 11.1.1: SELECT GLOBAL. Runtime, check the value of the tx_isolation system variable (note that the variable has been renamed transaction_isolation from MariaDB 11.1.1, to match the option, and the old name deprecated). To determine the global and session transaction isolation levels at Level to REPEATABLE READ, use these lines in the For example, to set the default isolation Rather than spaces, so the allowable values are READ_UNCOMMITTED, Values of level for this option use dashes transaction-isolation=level option on the command line or in an option file. To set the global default isolation level at server startup, use the Session isolation level (even in the middle of a transaction), or the isolation The statement sets the isolation level for the next (not started) transactionĪ change to the global default isolation level requires the Transaction level for all subsequent transactions performed within the With the SESSION keyword, the statement sets the default.Transaction level globally for all subsequent sessions. With the GLOBAL keyword, the statement sets the default.This statement sets the transaction isolation level or the transaction access mode globally, for the current session, or for the next transaction:
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